This research will investigate the biology of the cochlea at the molecular level. It will focus on several small molecules [amines such as Unk 2.5 and glutamate] found in the cochlea of guinea pig. The hypothesis to be tested is that these small molecules have functions in the cochlea, aside from metabolic. Based on the premise that the levels of these molecules in the extracellular space of the cochlea (perilymph) reflect certain cellular activities, then it follows then that evidence for or against various cellular activities, can be obtained by determining the concentrations of the molecules in the perilymph compartment under different treatments. This will be accomplished by determining: (1) the identity of the molecules utilizing techniques such as ionization mass spectrometry; and (2) treatments, such as exposure to intense sound the sectioning the efferents, which may alter the levels of these molecules int he perilymph. The experiments extend discoveries made during the previous grant. These questions are important because the molecules may have a role in cellular damage and hearing loss.